What is the term for the tendency of water to rise in a thin tube?

• A. Capillary Action
• B. Osmosis
• C. Diffusion
• D. Transpiration

Answer: (A)

Capillary action is the tendency of water to rise in a thin tube. This happens because water molecules are attracted to the tube’s surface (adhesion) and to each other (cohesion). In a narrow tube, these adhesive and cohesive forces pull the liquid upward against gravity, creating a curved meniscus that climbs the walls and elevates the water column. The height reached depends on the tube’s radius, the liquid’s surface tension, and the contact angle, with smaller radii and stronger adhesion producing a taller rise. This concept helps explain how water moves through tiny vessels in plants and through small gaps in soils and porous materials. Osmosis, diffusion, and transpiration involve different processes—water moving across membranes, spreading due to concentration differences, and water loss from leaves, respectively—and do not describe water rising in a thin tube.